Knowledge is a key part of animal care. Sure, the physical work plays a large role, but a solid understanding of your chickens’ physiology is important for ensuring you provide the best care you can. Plus, you’ll increase your own enjoyment of farming when you take the time to learn some of the fascinating biology of these animals that you spend so much time with. To that end, we’ll take a “look” at one very interesting attribute of your chickens: their eyesight.
At first, you might not think there would be much to say about the topic. Chickens have eyes, and aren’t they pretty much like ours?
There certainly are some similarities between human and chicken vision. But chicken vision is substantially different from ours, and understanding the hows and whys can help explain some unique chicken behaviors.
People have what is called binocular vision. The word “binocular” in everyday use might imply magnification. But in biology, binocular vision just means that both eyes work together to form a single image.
It’s not that you can’t see with just one eye, but both eyes are designed to function in tandem and produce a 3D image with depth perception. And, all things being equal, two eyes focusing together produce a sharper image.
But chickens have monocular vision. While they still have two eyes, of course, the eyes are widely separated on each side of the head. The advantage here is that the chicken picks up an extremely wide field of vision—300 degrees, compared to a human’s 180.
A wide field of vision is typical of prey animals (such as chickens), as it helps them watch for predators in more directions at once. While chickens’ vision does overlap a little bit in front of their beak, this binocular portion is limited. The key takeaway is that chickens’ eyes can focus on and form two completely different images in their brain.
Different Eyes for Different Tasks
In chickens, each eye sees different views and is designed for different uses. Surprisingly, a chicken’s left eye excels at focusing on distant objects (such as keeping a watch on the environment), while the right eye is good at close focus (such as when searching for objects on the ground). And chickens can multitask in this way, looking at and observing two different things at once.
This difference in focusing abilities develops while the chick is still inside the egg. Chicks orient themselves so that the left eye is against their body and the right eye is near the semitransparent eggshell.
This results in two different near- and far-sighted eyes and explains why chickens tend to tilt their heads to the left side when looking up at something.
Chickens need to notice and track moving objects for a couple of reasons. First, it helps them find little insects on the ground. Secondly, it aids in watching for predators. Fortunately for the chickens, a double cone structure in their retinas provides them with better motion perception than we have.
They’re more attuned to motion and more likely to notice something moving.
There’s another, somewhat related factor. To borrow a term from video technologies, human eyes can detect motion at what we could call about 30 frames every second. Flickering devices such as a TV, computer screen and LED lights operate at a higher rate than this—about 60 hertz—to ensure your eyes perceive the flicker as smooth motion and constant light.
But your chickens’ vision is completely different. They can see about 150 to 200 frames per second (and thus wouldn’t enjoy watching TV too much!). As a result, you should only light your coop with LED bulbs with a high refreshing rate.
Understanding color in your chickens’ vision requires a quick science lesson, but one worth taking. Briefly, what we typically refer to as “light”—meaning the shining sun and all of the colors of the world—is just one small piece of the much broader electromagnetic spectrum.
When you look at a rainbow, you see all the wavelengths of colors lined up neatly: violet, blue, green, yellow, orange, red. Our eyes are receptive to that specific portion of the spectrum. But other wavelengths of “light” are out there that we can’t see—such as radio waves or X-rays, for example.
Chickens vision is interesting because they can perceive ultraviolet light—a wavelength that is just below violet on the spectrum. This is in addition to the standard set of colors that humans can see. It’s impossible to imagine what this must look like to the chickens, but we can make some educated guesses.
Chickens can probably look at a rainbow and see an additional band. But there are other, more practical advantages.
Certain foods that chickens forage for (such as insects, seeds and some fruits) are all easier to see in ultraviolet light, especially when foliage is surrounding them. So seeing in this wavelength helps chickens locate their next meal. Feathers also have a distinctive look in ultraviolet light, and mother hens may use this fact to evaluate which chicks are developing properly (i.e., growing feathers the fastest).
In some other bird species, ultraviolet light reveals unique feather patterns, making it possible for the birds to differentiate males and females even when there isn’t a visible difference to humans.
Because of this ability to detect ultraviolet light, avoid fluorescent light fixtures in your coop, as the chickens would be able to see an annoying flicker from this type of device.
That Third Eyelid
Photographers who work with chickens (such as me!) quickly learn that these birds possess a unique eye feature that humans don’t: a third eyelid called the nictitating membrane. If you’ve ever taken even a few photographs of a chicken, you’ve probably seen how the third eyelid invariably shows itself, creating an unusual semitransparent appearance over the surface of the eye.
The membrane, which is found in plenty of birds, reptiles and some mammals (dogs have one), is primarily used to protect the eye, to clean it, to lubricate it and even to aid in healing. It functions almost like a biological windshield wiper, drifting across the eye horizontally and then back again.
The transparent feature allows the chicken to see through the third eyelid while it’s closed. Some birds use it as a built-in safety feature when pecking or feeding young.
Not Much Eye Movement
Chickens generally tend to move their heads in a rather quick, jerking fashion. If they want to look at something new, they usually do so with a rapid head turn.
Part of the reason behind this is that chickens don’t rely much on eye movements. They can turn their eyes from side to side the way we do, but they don’t do it nearly as much and instead opt to turn the entire head.
Read more: Check out these fun chicken facts!
Poor Night Vision
For all their advantages, a chicken’s eyes are lacking when it comes to night vision. Humans don’t have fantastic night vision either, especially when compared to cats. But we see substantially better in the dark than chickens.
This lack of solid night vision is probably a major reason why chickens are perfectly content to quietly wait through the night in their coop and are not nocturnal.
Your chickens are amazing birds—and they are amazingly suited for seeing the world in a chicken-specific way that is beneficial to them and interesting to us. The next time you’re out in the coop enjoying your flock, don’t just rush through your chores—take a minute to think about the fascinating biology of your birds, especially their unique vision.
The Pineal Gland
While unrelated to vision, it’s worth noting that the light-sensitive pineal gland in a chicken’s brain can be stimulated through the skin. So even a chicken who is blind visually is still capable of perceiving day/night changes and seasonal lighting effects.
Hens adjust their egg production based off of this and produce fewer eggs as winter approaches.
This article originally appeared in the January/February 2023 issue of Chickens magazine.